1. Field of the Invention
This invention relates generally to data recording disk drives, such as magnetic recording hard disk drives, and more specifically to such disk drives that experience track misregistration, for example, due to out-of-plane disk vibration induced by air flow during rotation of the disks.
2. Background of the Invention
Data recording disk drives have a stack of recording disks rotated by a spindle motor, and an actuator that moves the read/write heads across the surfaces of the rotating disks. Each read/write head is formed on an air-bearing slider attached to one end of a flexible suspension. The suspension is attached at its other end to a relatively rigid arm of the actuator and allows the slider to pitch and roll on a bearing of air generated by the rotating disk. The disk drive actuator is typically a rotary voice coil motor (VCM) that moves the actuator arm and the attached suspension and slider generally radially to position the head at the desired track under the control of a servo control system that receives pre-recorded servo position information from the disk. The trend in future disk drives is a continual decrease in the spacing of the concentric data tracks on the disk to increase the data storage density, and a continual increase in the rotational speed of the disk stack to decrease the data transfer time. As storage densities and rotational speeds increase, the ability to position the read/write heads to the proper data tracks and maintain the heads on the data tracks becomes more difficult. As disk-stack rotational speed increases, air-flow turbulence near the perimeter of the disks increases, which causes out-of-plane buffeting or vibration of the disks (sometimes misleadingly called disk “flutter”). These vibrations cause track-misregistration (TMR) of the read/write heads and thus errors in reading data from and writing data to the data tracks.
To address the problem of TMR caused by air-flow-induced disk vibration, thicker disks have been proposed, because disk vibration amplitude reduces as the thickness of the disk increases. However, there is limit on the maximum disk thickness due to the total height limitation of the disk drive. Shrouds located around the disk stack have also been proposed to reduce the effect of air flow turbulence on the disks, but have been shown to reduce disk vibration amplitude by only about 25% or less. Disk vibration damping plates have also been proposed, as described in published U.S. Patent Application US 2003/0072103 A1. The damping plates have planar surfaces parallel to the planar surfaces of the disks and extend between the disks near their perimeter to encourage laminar air flow and thus a reduction in air flow turbulence. However, the damping plates also cause high viscous shear forces on the disks, which require a higher spindle-motor torque, and thus higher power consumption, to maintain the desired high rotational speed.
What is needed is a disk drive with a substantial reduction in disk-vibration-induced TMR of the read/write heads.